Conventionally, for an insulated covering material for an insulated wire used in carrying out wiring of parts for a car such as an automobile, electric/electronic equipment and the like, generally in wide use is a vinyl chloride resin excellent in flame retardancy, into which additives such as a plasticizer and a stabilizer are blended as appropriate, and adjustments are made to types and blending amounts of these additives according to a variety of required properties including mechanical properties such as wear resistance, tensile strength and tensile elongation, flexibility, and workability.
However, there is a problem that the vinyl chloride resin, having flame retardancy by itself, includes halogen elements in its molecular chains, so that it emits harmful halogenous gas into the atmosphere in case of car fire or at the time of combustion for disposing of electric/electronic equipment by incineration, causing environmental pollution.
Under these circumstances, developed these days has been a so-called non-halogenous flame-retardant resin composition, which is prepared by using polyethylene, polypropylene or the like as its base resin and adding a metallic hydrate such as magnesium hydroxide as a flame retardant; however, there is a disadvantage that mechanical properties such as wear resistance remarkably degrade since the non-halogenous flame-retardant resin composition requires a large amount of metallic hydrate to be added thereto as the flame retardant.
Thus, in order to overcome such a disadvantage, for example, Japanese Patent Gazette No. 3280099 discloses an art to use a plurality of polyolefin resins and rubbers as the base resin, in which a specific functional group is further contained by a specific amount, so as to increase an affinity between the base resin and the metallic hydrate to improve the mechanical properties such as wear resistance.
However, the conventionally-known non-halogenous flame-retardant resin composition is turned out to cause problems as described below in a case where it is used as an insulated covering material for an insulated wire while possessing flame retardancy, mechanical properties, flexibility, workability and heat resistance.
Generally, in the case of using the insulated wire in a car such as an automobile, it is often the case that a plurality of insulated wires are tied in a bundle to be made into a wire bundle, around which a protective material in various shapes such as a tape, tube or sheet is wound to be utilized as a wiring harness.
At this time, as the insulated wires making up the wiring harness, not only non-halogenous insulated wires in which non-halogenous flame-retardant resin compositions are used as insulated covering materials are used, but also vinyl chloride insulated wires and the like in which vinyl chloride resin compositions such as polyvinyl chloride are used as insulated covering materials are abundantly used, empirically.
Therefore, the situation is such that mixed use of the non-halogenous insulated wires and the vinyl chloride insulated wires is difficult to completely avoid; however, use of the non-halogenous insulated wires in contact with the vinyl chloride insulated wires and the like under such a situation is turned out to cause a problem of remarkably deteriorating the insulated covering material for the non-halogenous insulated wires in the wire bundle to degrade its heat resistance.
Further, since the vinyl chloride resin composition and the like are usually used as a base material for the wiring-harness protective material wound around the wire bundle, use of the non-halogenous insulated wire in contact with a vinyl-chloride wiring-harness protective material and the like is turned out to cause the same problem.
The causes of the problems are not found in a detailed mechanism, however, the problems are assumably caused because an antioxidant in the insulated covering material consisting of the non-halogenous flame-resistant resin composition is remarkably consumed, or the antioxidant itself makes a transition into the vinyl chloride insulated wire or the vinyl-chloride wiring-harness protective material when the vinyl chloride insulated wire, the vinyl-chloride wiring-harness protective material or the like comes into contact with the non-halogenous insulated wire. At any rate, there is a need to immediately solve these problems concerning deterioration.
Consequently, the present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a non-crosslinked flame-retardant resin composition which possesses sufficient flame retardancy, mechanical properties, flexibility and workability, and also possesses excellent heat resistance without deteriorating over a long period of time.
In addition, another object of the invention is to provide a non-halogenous insulated wire in which the above-described non-crosslinked flame-retardant resin composition is used as an insulated covering material, and a wiring harness including the non-halogenous insulated wire.